1. Field of the Invention
This invention relates to a composite for use in reinforcing roofing membranes made from bituminous materials. The use of this invention by manufacturers of such membranes results in significantly easier processing with less-complicated equipment. Moreover, sufficient strength in the roofing membranes can be achieved with less reinforcing material than previously used. The membranes can also be made significantly thinner, which is not only a saving in the amount of bituminous raw material required and a reduction in the weight load on the roof after installation, but also increases flexibility so that handling during installation involves a decreased risk of creating cracks or other weaknesses which could lead to leaks.
2. Description of the Prior Art
Asphalt-like roofing membranes, such as those which are used on flat roofs, have been made from bituminous materials reinforced with three separate layers of reinforcing materials: polyester mat, non-woven fiberglass scrim held together with a thermosetting adhesive, and fiberglass mat. Other combinations of separate layers used previously have included (a) fiberglass mat and fiberglass scrim, (b) fiberglass mat and polyester scrim, and (c) polyester mat and fiberglass scrim. These reinforcing layers have been unwound from their respective separate rolls and led together through a tank or vat of heated bituminous material using methods which are known in the art. We are using "mat" in its usual meaning of an entangled mass of filaments and "scrim" in its usual meaning of an open fabric. The bituminous material has been a "modified bitumen" such as asphalt combined with about 20% by weight of atactic polypropylene or 5 to 15% styrene butadiene styrene rubber. The bituminous material has acted as an adhesive to hold the layers within the membrane. In addition, we have suggested replacing the polyester mat in the combination of polyester mat, fiberglass scrim, and fiberglass mat with a composite polyester layer consisting of a polyester scrim coated with polyvinyl chloride bonded to a light weight polyester mat; we understand that such a roofing membrane has been made and sold for more than a year.